This invention relates generally to processes for aerating suspensions. More particularly, the present invention relates to processes for flotating suspensions.
It is known that operation of a flotation cell can be controlled by means of the liquid level in the flotation cell, the amount of foam overflowing, and the throughput, where the throughput is pre-defined by the required production level.
Known control systems have the disadvantage that they are relatively inflexible. In particular, it is difficult with the control systems known to achieve a favorable compromise between the quality of the accept leaving the cell on the one hand and the energy input and loss of potentially recyclable materials on the other.
DE 42 25 117 C1 presents a control system in which, among other things, the foam back-up height in the foam channel of a primary flotation cell is measured and the amount of accept leaving the primary cell controlled on the basis of this measurement, thus the back-up height in the foam channel of the primary flotation cell remains constant. According to a similar principle the proportion of backfeed to the primary cell is also controlled in the secondary cell, based on the level height in the foam channel to the secondary cell.
This process, however, also does not provide a more flexible means of controlling operation in a flotation cell.
The problems with the state-of-the-art processes also occur in flotation of pulp suspensions, particularly in deinking flotation.
Deinking flotation is a process for removing contaminants and printing ink particles from pulp suspensions, particularly those produced in waste paper treatment. In this process, hydrophobic solids, such as printing ink particles or stickies, are brought into contact with gas bubbles in a suitable flotation cell. The solids adhering to them are carried to the surface of the liquid along with the gas bubbles and can be removed there as foam. Since the pulp is hydrophilic, it is discharged together with the accept. As there is no 100% separation of fibers and ink particles or stickies, there is a direct relation here between the losses and the cleaning effect achieved.